Physical quantity sensor, electronic apparatus, and vehicle

Abstract

A physical quantity sensor includes a first element section in which first capacitances varying in accordance with a physical quantity have first saturation capacitance values at which the first capacitances are saturated by a first physical quantity, a second element section in which a second capacitances varying in accordance with the physical quantity have second saturation capacitance values at which the second capacitances are saturated by a second physical quantity smaller in absolute value than the first physical quantity, a multiplexer for outputting the first signals from the first element section and the second signals from the second element section, and a determination circuit that determines whether or not the level of the second signal input via the multiplexer reaches a threshold value which is a level of the second signal when the second physical quantity acts.

What is claimed is: 
     
       1. A physical quantity sensor comprising:
 a first element section which includes a first capacitance varying in accordance with a physical quantity, and in which the first capacitance has a first saturation capacitance value at which the first capacitance is saturated by a first physical quantity; 
 a second element section which includes a second capacitance varying in accordance with the physical quantity, and in which the second capacitance has a second saturation capacitance value at which the second capacitance is saturated by a second physical quantity smaller in absolute value than the first physical quantity; 
 a drive circuit configured to output a drive signal to the first element section and the second element section; 
 a multiplexer configured to output a first signal from the first element section and a second signal from the second element section; and 
 a determination circuit that determines whether or not the level of the second signal input via the multiplexer reaches a threshold value which is a level of the second signal when the second physical quantity acts. 
 
     
     
       2. The physical quantity sensor according to  claim 1 , wherein
 the absolute value of the second physical quantity is 50 through 90% of the absolute value of the first physical quantity. 
 
     
     
       3. The physical quantity sensor according to  claim 1 , wherein
 the first signal and the second signal are same in absolute value of level as each other and opposite in sign to each other to form a differential signal pair. 
 
     
     
       4. The physical quantity sensor according to  claim 1 , wherein
 the second signal is a signal proportional to a combined capacitance of the first capacitance and the second capacitance. 
 
     
     
       5. The physical quantity sensor according to  claim 1 , wherein
 the drive circuit stops outputting the drive signal when the level of the second signal reaches the threshold value. 
 
     
     
       6. The physical quantity sensor according to  claim 1 , further comprising:
 an interface circuit, wherein 
 the interface circuit outputs a determination result when a signal from the second element section reaches the threshold value based on a determination signal from the determination circuit. 
 
     
     
       7. The physical quantity sensor according to  claim 6 , further comprising:
 a self-diagnostic circuit configured to perform a self-diagnosis of the first element section, wherein 
 the self-diagnostic circuit generates a test signal to be input to the first element section, and then diagnoses presence or absence of an abnormality in the first element section based on a signal output from the first element section in response to the test signal. 
 
     
     
       8. The physical quantity sensor according to  claim 7 , wherein
 the interface circuit outputs a caution signal when the self-diagnostic circuit determines an abnormality. 
 
     
     
       9. The physical quantity sensor according to  claim 7 , wherein
 the self-diagnostic circuit operates based on a command input to the interface circuit. 
 
     
     
       10. The physical quantity sensor according to  claim 7 , further comprising:
 an external terminal, wherein 
 the self-diagnostic circuit operates based on a trigger signal input to the external terminal. 
 
     
     
       11. An electronic apparatus comprising the physical quantity sensor according to  claim 1 . 
     
     
       12. A vehicle comprising the physical quantity sensor according to  claim 1 .